1. Field of the Invention
The present invention relates to ink composition, and particularly, to an ink composition with high heat resistance for imprint lithography and roll printing, capable of forming accurate fine patterns, and a method of fabricating a liquid crystal display (LCD) device using the same.
2. Background of the Invention
Recently, as information displaying becomes more attractive and demands on the use of portable information media increase, studies and commercialization of lighter, thinner flat panel displays (FPDs), substituting a cathode ray tube (CRT) as the existing display device, have been broadly conducted. Especially, among the FPDs, a liquid crystal display (LCD) device is to display images by using optical anisotropic property of liquid crystal. The LCD device is excellent in resolution, color rendering property, image quality and the like, and thus widely being applied to notebooks, desktop monitors and the like.
The LCD device includes a color filter substrate, an array substrate, and a liquid crystal layer interposed between the color filter substrate and the array substrate.
An active matrix method, which is a normally used driving method in the LCD device, is configured to drive liquid crystal of pixel units by employing amorphous silicon thin film transistors (a-Si TFTs) as switching devices.
Hereinafter, a structure of a related art LCD device will be described in detail with reference to FIG. 1.
FIG. 1 is a disassembled perspective view schematically showing a related art LCD device.
As shown in FIG. 1, the LCD device includes a color filter substrate 5, an array substrate 10, and a liquid crystal layer 30 interposed between the color filter substrate 5 and the array substrate 10.
The color filter substrate 5 is provided with a color filter C having a plurality of sub color filters 7 for rendering red (R), green (G) and blue (B) colors, a black matrix 6 for dividing between adjacent sub color filters 7 and blocking light transmitted through the liquid crystal layer 30, and a transparent common electrode 8 for applying a voltage to the liquid crystal layer 30.
Also, the array substrate 10 is provided with a plurality of gate lines 16 and data lines 17 arranged in horizontal and vertical directions for defining a plurality of pixel regions P, thin film transistor T as switching devices formed at intersections between the gate lines 16 and the data lines 17, and pixel regions 18 formed on the respective pixel regions P.
The color filter substrate 5 and the array substrate 10 having such structure are attached to face each other by a sealant (not shown) formed at an outer periphery of an image display region, thereby constructing an LCD panel. The attachment between the color filter substrate 5 and the array substrate 10 may be implemented by an attachment key (not shown) formed either at the color filter substrate 5 or at the array substrate 10.
The fabrication of the LCD device includes plural times of a photolithography process required to produce the array substrate having TFTs.
Also, for forming fine patterns, which are applied to information storage, compact sensors, photonic crystal and optical elements, micro-electro mechanical systems, display devices and semiconductors, the photolithography process conducted to form fine patterns using light is performed.
The photolithography process denotes a series of processes by which patterns printed on a mask are transferred on a thin film-deposited substrate so as to form desired patterns. The photolithography process is implemented through a plurality of complicated processes including photoresist coating, alignment and exposure, development and the like.
First, after coating photoresist as a photo resistor on a thin film on which preset patterns are to be formed, a pattern-formed photomask is aligned with the thin film and then exposed to light. Here, the photomask used is divided into a preset transparent region and a blocking region. Light transmitted through the transparent region may chemically change the photoresist.
The chemical change in the photoresist may depend on a type of photoresist. For a positive photoresist, regions exposed to light become soluble in a developer solution. To the contrary, for a negative photoresist, regions exposed to light become insoluble in the developer solution. The description will exemplarily be given herein of the case of using the positive photoresist.
Following the exposure process, the exposed regions of the photoresist are removed by a developer solution, thereby generating preset photoresist patterns on the thin film.
Afterwards, the thin film is etched to be conformable with the photoresist patterns and the rest of photoresist patterns are then removed, thereby making a preset form of thin film patterns.
In the photolithography process, a linewidth of a circuit or pattern is determined according to wavelength of light used in the exposure process. Considering the current technical standard, it is difficult to form fine patterns less than 70 nm on a substrate through the photolithography process due to light interference.
Further, as patterns are getting supermicronized, an initial investment cost is increased due to an expensive exposure equipment, masks with high resolution are required and the like, resulting in excessively increasing process cost. In addition, since the complicated process, including exposure, baking after exposure, development, baking after development, etching, washing and the like, should be carried out every time forming patterns, it takes a long time to carry out such processes and the photolithography process should be repeated plural times, thereby lowering productivity.
To solve such problems, an imprint lithography and a roll printing have been introduced. The imprint lithography is a method, initially invented by Stephen Chou et al. from the Princeton University in the United States, for carving nano-scaled patterns. According to this method, desired forms are previously made on a surface of inorganic material or polymer with relatively strong intensity and then fine patterns are formed as the previously made forms are affixed onto another material. In detail, an inorganic material or polymer mold having desired fine patterns pre-formed thereon is attached onto a curable composition coated on a metallic film or an organic layer to be thermally cured or photocured, thereby forming patterns. This method has advantages in a simple process and an effective fine pattern formation, compared to the existing photolithography.
The roll printing method has been disclosed, for example, in Korean Patent Application No. 2006-0005482 (Laid Open Application No. 10-2007-76292), entitled “roll printing apparatus and method of fabricating display device using the same.” According to the roll printing method, in place of the high resolution mask used when forming patterns through the existing photolithography, silicon polymer and cliché are used to transfer patterns directly on a substrate to desirably form fine patterns thereon, thereby forming the fine patterns.
However, in a low temperature baking process after the fine pattern formation, a problem of disappearance of a metal substrate, which is to be protected upon etching process may be caused by a decrease in adhesive force between an ink composition and a substrate to desirably form patterns thereon. Furthermore, in a high temperature baking process, the adhesive force between the substrate to desirably form patterns thereon and the ink composition is increased but a pattern linewidth and line interval formed by the ink composition runs down to occur deformation, which may cause an excessive defect, for example, defective patterns, resulting in limitation on a consecutive transfer of fine patterns and difficulty in an enhancement of accuracy of the fine patterns.